WO2012011013A2

WO2012011013A2 - Improvements in phototherapy

Info

Publication number: WO2012011013A2
Application number: PCT/IB2011/053049
Authority: WO
Inventors: Gerrit Oversluizen; Liesbeth Van Pieterson; Frank Anton Van Abeelen; Guofu Zhuo
Original assignee: Koninklijke Philips Electronics N.V.
Priority date: 2010-07-22
Filing date: 2011-07-08
Publication date: 2012-01-26
Also published as: WO2012011013A3

Abstract

An apparatus (27) for bio-stimulating phototherapy is herewith provided. The apparatus comprises a light source (29) for providing light with a phototherapeutic wavelength and a controller (37). The apparatus is configured for illuminating the skin (3)of a subject's body portion (1) with light emitted by the light source. The controller is configured to control operation of the apparatus, in particular the light source, such that the light is provided in a series of optical pulses with a controlled pulse repetition rate, with the pulses having a controlled pulse irradiance and pulse duration. The controller is configured to control the pulse irradiance the pulse duration and the pulse repetition rate as a function of at least one of the melanin index (M) and the lightness (L*) of the skin to provide an effective time averaged irradiance at or below a predetermined value. A method is also provided.

Description

Improvements in phototherapy

TECHNICAL FIELD OF THE INVENTION

The present disclosure relates to phototherapy, in particular to apparatus and methods for dermatological phototherapy. The apparatus and methods may be used both in professional and domestic use, and for curative, cosmetic and wellness purposes.

BACKGROUND OF THE INVENTION

Phototherapy, treating a patient with light, is known for treatment of various conditions. It has been found that optical absorption of the skin may affect treatment efficiency. Both ultraviolet (UV) and/or infrared (IR) treatments have proven to be able to cause damage to the skin when the radiation absorbed by the skin exceeds a threshold.

UV treatment is often used in treatment of various dermatological diseases such as e.g. psoriasis. The main problem of UV treatment is that the absorbed UV radiation can cause DNA damage and skin cancer when the irradiation dose is too high. Often a MED value (minimum erythemal dose) is used as a guide to determine a safe UV dose. The MED is the smallest dose to produce visible reddening of the skin, which is indicative of a skin irritation. The MED is known to vary with skin type. For characterizing skin type, the Fitzpatrick scale is commonly used. However, large differences in MED are found between different individuals of the same Fitzpatrick type, requiring determination of the MED by applying different amounts of light to the skin and observing at what dose erythema has occurred. This method inherently imposes irritation and potential damage to the tested skin portion.

Infrared (IR) phototherapy is often used in the context of hair removal (depilation), where a sufficient amount of heat energy is needed near the hair shaft and hair bulb to 'burn' the hair. Such treatment should be performed without damaging the skin through energy absorption. The correct amount of energy deposition is generally determined by trial and error.

GB 2 381 752 discloses a skin treatment apparatus having a laser radiation source for delivering coherent radiation to skin to be treated, a sensor for sensing at least one property of the skin and a controller. The controller is operable to control the radiation emitted from the laser radiation source in response to the property or properties sensed by the sensor. Preferably, the radiation source comprises a pulsed laser diode and the controller is operable to control at least one of its energy, pulse width and pulse interval. The sensor may be a pigment sensor, preferably a single chip blue, red and yellow detector, a pH sensor or a temperature sensor. The apparatus is particularly suitable for the removable of hairs from the skin. A method of treating skin with laser radiation comprises sensing at least one property of the skin and delivering laser radiation to the skin according to the sensed property or properties.

Such apparatus relies on thermal effects of light therapy and it is proposed to use two lasers in parallel in order to target parts of the epidermis at different depths.

A presently increasingly relevant field - and being the field of the present disclosure - is that of bio-stimulation of living tissue. Bio-stimulating skin phototherapy may be applied for treating jaundice and psoriasis and may comprise curative phototherapy like wound healing or cosmetic phototherapy like rejuvenation. A particular branch of bio- stimulating phototherapy is known as Low Level Light Therapy (or: LLLT). In the field of bio-stimulation of living tissue, any damage to the tissue must be prevented. This poses significantly stricter requirements on the applied dose, since doses that are considered acceptable for hair removal may in fact already exceed stimulatory effective thresholds. However, reducing the applied illumination doses for safety reasons can easily lead to administration of a dose that is therapeutically ineffective. Successful treatment may thus require individual adjustment of dose and protocol. The MED indicates an upper dose limit but provides no useful information for doses below the MED. Indeed, for bio-stimulatory treatments clinical test results based on MED or the Fitzpatrick scale have proven

inconclusive.

Consequently, there is a desire for equipment and methods for providing both safe and effective bio-stimulation phototherapy, in particular for domestic use.

SUMMARY OF THE INVENTION

An apparatus for bio-stimulating phototherapy is herewith provided. The apparatus comprises a light source for providing light with a phototherapeutic wavelength and a controller. The apparatus is configured for illuminating the skin of a subject's body portion with light emitted by the light source. The controller is configured to control operation of the apparatus, in particular the light source, such that the light is provided in a series of optical pulses with a controlled pulse repetition rate, with the pulses having a controlled pulse irradiance and pulse duration. The controller is configured to control the pulse irradiance, the pulse duration and the pulse repetition rate as a function of at least one of the melanin index M and the lightness L* of the skin to provide an effective time averaged irradiance at or below a predetermined value.

Due to the provision of the light in the form of optical pulses, the applied irradiance, the effective time averaged irradiance, and the total administered dose may efficiently be controlled substantially independently.

The apparatus may comprise an input system for determining the predetermined value of the effective time averaged irradiance, which enables use of the apparatus for different skin types or conditions, e.g. different curative stages, different degrees of tanning etc. and/or use for or by different subjects.

Melanin absorbs radiation, hindering attaining an intended treatment dose in the body portion. The melanin index M indicates the melanin content in the skin considered and the lightness L* is defined in 1976 by the Commission International d'Eclairage (CIE) and is a measure of how the human eye perceives the lightness of the skin, see M.D. Shriver and E.J. Parra, "Comparison of Narrow-band reflectance spectroscopy and tristimulus colorimetry for measurements of skin and hair color in persons of different biological ancestry", Amer. J Phys Anthropology 112: 17-27 (2000). In humans, melanin is almost exclusively located in the epidermis. It has been found that by determination of the melanin index or the lightness the irradiation losses in the epidermis may be assessed, and that for deeper-lying tissue (e.g. dermis, hypodermic tissue) absorption losses due to melanin are of little to no influence. Hence, the actually administered phototherapeutic dose into these deeper-lying tissues can be reliably assessed. Determining the melanin index or the lightness of the skin portion provides quantitative information on, and determination of, the effective filtering function of the skin due to the melanin. The melanin index M may be measured by apparatus commonly used in cosmetic industry, e.g. the Skin Pigmentation Analyzer © SPA 99 of CK electronic GmbH, or the DSM II ColorMeter by Cortex Technology, which latter apparatus can measure both the melanin index M and the lightness L*.

Measurement of the melanin index is preferred over measuring the lightness since it has been found that the melanin index is a more reliable parameter for quantifying the melanin content of the skin, see Shriver and Parra cited above.

By determining the irradiance as a function of the melanin index, the irradiance that is effectively deposited in the dermis and hypodermic tissue can be accurately determined. This allows reliable treatment. By determining the pulse duration and the pulse repetition rate, together defining a duty cycle, as a function of the melanin index, the absorption of the deposited irradiation energy by the skin, in particular the epidermis, can be determined and heating of the skin due to the treatment can be predicted. Heating over a predetermined value, which may result in damage and/or pain, can thus be prevented.

Further, a method of bio-stimulating phototherapy of a subject's body portion is provided herewith. The method comprises the steps of determining a bio-stimulating wavelength range to be administered, determining a first irradiance to be applied;

determining at least one of the melanin index and the lightness of the skin of the body portion; determining a second irradiance as a function of the first irradiance, the wavelength range and the melanin index; providing a number of optical pulses of the determined wavelength range to the body portion, each pulse having a pulse irradiance, a pulse duration and a pulse repetition rate. The pulse irradiance, the pulse duration and the pulse repetition rate are controlled as a function of the melanin index and/or the lightness, respectively, of the skin and an effective time averaged irradiance at or below a predetermined value is provided. The pulse irradiance is preferably controlled to the level of the second irradiance determined before.

The predetermined effective time averaged irradiance value may be a fixed or fixable value, e.g. approx. 40 mW/cm^"2 which may be tolerated by a skin having a relatively high thermal conductivity such as a healthy, well blood-perfused light Caucasian skin, approx. 30 mW/cm^"2, which is suitable for most Caucasian skin types, approx. 20 mW/cm^"2 which is suitable for dark skin types and sensitive light skin types and in particular cases approx. 10 mW/cm^"2 which is acceptable for nearly all people, including for damaged skin. For particularly sensitive skin and/or body parts, the effective time averaged irradiance value may be set even lower.

The effective time averaged irradiance value may be determined as a function of the melanin index, so as to provide a personalized value.

The function for calculating a phototherapy dose to be administered to the skin may comprise a wavelength and melanin- index dependent irradiance correction factor Icf = Icf(M, λ) = exp(Cm μ(λ) d), wherein Cm is a measure of the concentration of melanosomes in the epidermis of the skin portion which may be stated in terms of the melanin index M as Cm = (M-20)/150 and may be approximated in terms of the lightness L* as Cm = 1.925 - 0.44 ln(L*), μ(λ) describes the wavelength dependent absorption of the melanin and may be

3 33 1 1 3 33 1

approximated as μ(λ) = μ₀ λ^{" '} = 6.6 x 10¹¹ λ°·" in units of cm^" with λ in units of nm and wherein μο is the average absorption coefficient of a single melanosome, and wherein d accounts for the optical path in the epidermis. The thickness of the epidermis generally varies between about 0.4 mm to about 1.2 mm, taking scattering into account d may be in a range from about 0.004 to about 0.024 cm, averaging over thickness variations and scattering provides a generally applicable range of about 0.008-0.016 cm, and a practical approximation is d = 0.012 cm. The function Icf corresponds to the inverse of the attenuation of the radiation by melanin absorption and it provides an approximation of the modification function of the skin under consideration. The function is applicable to usefully provide correction factors over a large wavelength range, from UV to near IR wavelengths, and for substantially all skin types, ranging from light Caucasian type skin to dark Negroid type skin.

Advantageously, the melanin index or the lightness, respectively, is determined in a wavelength range between approx. 400 nm and approx. 2000 nm, in particular between approx. 500 nm and approx. 1500 nm, more in particular between approx. 600 nm and approx. 900 nm, and the body portion is illuminated with a phototherapy wavelength in that wavelength range.

It has been found than in the wavelength range between ca. 400-2000 nm several phototherapeutic treatments may be provided. From ca 450 nm, absorption of light by haemoglobin and oxyhaemoglobin generally decays with increasing wavelength. A local maximum is located between ca 550-600 nm with a steep decrease for longer wavelengths. On the other hand, absorption by water generally increases from ca 450 nm to 2000 nm with a number of absorption peaks near particular wavelengths, in particular around ca 1600 nm. Melanin has a generally decreasing absorption over the wavelength range 400-2000 nm. Between ca 500-1500 nm absorption of (oxy)haemoglobin and water is reduced and in the wavelength range of ca 600-900 nm the main absorber is melanin. However, since the wavelength dependent absorption profile of melanin is known and rather smooth, correction may also be effectively employed in wavelength ranges where (oxy)haemoglobin and water have a significant absorption influence.

The light source may comprise one or more light emitting diodes (LEDs). LEDs may provide light in various well-defined wavelengths (colors) at high efficiency and produce little heat compared to other light sources. The LEDs may therefore be placed close to the body portion. LEDs are generally well controllable with respect to output power and may be rapidly switched, enabling fine control over the operation of the apparatus. Moderate and high-power LEDs that do not exhibit superluminous or laser operation are particularly suited for use in bio stimulation since such LEDS do not exhibit a threshold-behavior in the emitted power and continuous power control is facilitated. A light source comprising plural LEDs facilitates a large effective surface area.

At least a portion of the apparatus may be formed to conform to at least part of the subject's body portion, e.g. by comprising a flexible, pliable or generally deformable portion such as a patch or bandage. The apparatus being formed for conforming to at least part of the body portion to be treated improves user comfort and allows prolonged treatment. Such apparatus, in particular in the form of a patch or bandage, may be worn inconspicuously under clothing. Such apparatus allows improved and predictable illumination of the body portion since shifted illumination portions and/or shadows caused by relative movement of the apparatus and the body portion are prevented. Further, illumination at an oblique angle may be prevented which may otherwise cause undesired reflection of the light and inaccurate dosing.

The apparatus may comprise at least one sensor for non-invasively determining the melanin index of a subject's skin portion. Advantageously, the sensor is connected with the controller. Thus, a compact integrated apparatus may be provided. Plural melanin index sensors may assist accounting for local melanin index variations, improving treatment efficiency and reducing accidental local overdosing.

The apparatus may comprise at least one further sensor for determining at least one further skin parameter. This allows additional control of and feedback on the treatment. An important parameter in phototherapy is the skin temperature. The further sensor may therefore suitably be a thermometer, e.g. a contact thermometer or an optical thermometer.

The apparatus may be configured for treating curative and cosmetic treatments. Examples are of wound healing, pain, psoriasis and skin rejuvenation, which conditions may be treated in a professional setting and/or in a domestic environment.

The controller may be configured to control the pulse irradiance, the pulse duration and/or the pulse repetition rate as a function of time during operation of the light source, so that a time- varying effective time averaged irradiance may be provided, which may be controlled as a function of one or more skin parameters, e.g. melanin index, in particular in case of prolonged treatment with near-UV light which may cause skin tanning, or blood flow affecting thermal balance of the skin, dryness or sweating, affecting reflection of the skin.

The controller may be programmable. The apparatus may comprise one or more user interfaces for programming the controller. The apparatus may comprise one or more interfaces for providing a program in a machine readable format for programming the controller, e.g. a card slot, a wireless data link etc.

These and other aspects will hereafter be elucidated with reference to the figures of the drawings, which indicate examples for explanatory purposes only. Various other embodiments may be conceived within the scope of the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

Fig. 1 is a schematic representation of a skin portion;

Fig. 2 indicates typical irradiance correction factors for different skin types;

Fig. 3 is a block scheme of an embodiment of a method of bio-stimulating phototherapy of a subject's body portion;

Figs. 4A-4C schematically show different pulse configurations;

Fig. 5 is a schematic side view of a phototherapy apparatus;

Fig. 6 is a schematic side view of another phototherapy apparatus.

DETAILED DESCRIPTION OF EMBODIMENTS

It is noted that in the drawings, like features may be identified with like reference signs. It is further noted that the drawings are schematic, not necessarily to scale and that details that are not required for understanding the present invention may have been omitted. The terms "upward", "downward", "below", "above", and the like relate to the embodiments as oriented in the drawings. Further, elements that are at least substantially identical or that perform an at least substantially identical function are denoted by the same numeral.

Fig. 1 illustrates illumination of a human body portion 1, showing a skin portion 3, and illumination light 5. The skin 3 comprises an epidermis layer 7 of ca 0.1 mm thickness, a ca 1-4 mm thick dermis layer 9 covering hypodermic tissue 11. A fraction of the illumination light 5 penetrates into the dermis 9, and another fraction may penetrated into the hypodermic tissue 11 indicated with the arrows 13 and 15, respectively.

In the epidermis 7, the main optical absorbers are melanin and water. In the dermis 9, the main optical absorbers are water and blood. Hence, the absorbing or filtering effect of melanin is concentrated in the epidermis 7. It has now been found that once the reduction in optical energy by the epidermis 7 is known, the fraction of the energy available for deposition in the dermis 9 and hypodermic tissue 11 can be calculated. It has further been found that determining the melanin index of the skin portion 3 in fact returns the melanin index of the epidermis 7 and thus provides a reliable quantification of the filtering effect of the epidermis 7 and determination of the dose available for deeper-lying tissue. Similarly, the absorption of the illumination light 5 by the melanin can be readily determined and heating of the epidermis 5 can be predicted to prevent overheating or hurting.

The filtering effect of the melanin in the epidermis can be substantial. The resulting correction factor Icf for different skin types are indicated in Fig. 2: light Caucasian skin with M = 26 (full lines), Asian skin with M = 42.5 (dotted lines) and dark Negroid skin with M = 80 (dashed lines). From Fig. 2 it becomes clear that the irradiance dose to be applied onto the skin may be a large multiple of the dose to be deposited in the dermis or hypodermic tissue, in particular for phototherapy with blue light for Asian or Negroid skin types.

The dose is a combination of illumination irradiance and illumination time. Adapting the irradiance and the dose to the local melanin index of the subject's skin will significantly affect and improve the effectiveness of the phototherapy. Also, safety of phototherapy is improved since irritation, damage and/or pain are substantially prevented. Phototherapy may therefore be made available for domestic use with little to no risk of damage or maltreatment.

An operating scheme of an embodiment of the method is provided in Fig. 3. A phototherapeutic wavelength (range) λ is selected and a suitable dose Dl and irradiance II to be administered to the body portion 1 are determined in step 17, e.g. by a practitioner. As an example, D. Barolet, "Light-emitting diodes (LEDs) in dermatology", Semin Cutan Med Surg 27:227-238 (2008), elucidates on the existence of suitable wavelengths and optimal doses or fluences for different phototherapies, dependent on the tissue and condition to be treated. An overview of conditions which may be treated with bio-stimulating phototherapy, the mechanism believed to underlie the treatment effect and the associated wavelengths is provided in the following table: Table 1. Phototherapy condition, mechanism (proposed) & action spectrum

1. J. Liebmann, M. Born, and V. Kolb-Bachofen, "Blue-light irradiation regulates proliferation and differentiation in human skin cells", J. of Investigative Dermatology 130(2010) 259-269.

2. C.V. Suschek, C. Oplander, E.E. van Faassen, "Non-enzymatic NO production in human skin; effect of UVA on cutaneous NO stores", Nitric Oxide 22(2010)120-135.

The melanin index M of the skin portion 3 of the body portion 1 is determined in step 19. This may be performed by measuring light reflectance of the skin portion 3 at one or more wavelengths and deducing the skins absorbance at the used wavelength(s). Using plural wavelengths facilitates removing contribution to the absorption by (oxy)haemoglobin and/or water.

In step 21 the absorption of light at the phototherapeutic wavelength (range) λ to be used is determined and the factor Icf is calculated according to the above-reference formula. Further, based on the wavelength (range) λ and the melanin index, the energy absorption of the epidermis is calculated and an effective time averaged irradiance Iav(M, λ) which is considered acceptable by the subject is determined. In step 23 a phototherapy dose D2 and a second irradiance 12 to be applied onto the skin portion 3 are calculated based on the dose Dl and irradiance II to be administered, respectively. This may comprise straightforward multiplication with the correction factor Icf, e.g.: D2(D1, Icf) = D2(D1, M, λ) = Icf(M, λ) * ϋΐ(λ) and 12(11, Icf) = 12(11, M, λ) = Icf(M, λ) * Ι1(λ). More complicated calculation is also conceivable. The phototherapy dose D2 may be applied by suitable selection of irradiance 12 and duration, which may comprise illumination in one or more pulses of which the pulse irradiance, duration and interval may be selected.

In step 24, based on the determined allowable effective time averaged irradiance Iav(M, λ) and the second irradiance 12, a pulse irradiance Ip (in [mW/cm ²]), a pulse duration Dp (in seconds [s]) and a pulse repetition rate Rp (in pulses per second [s ¹]) are determined, wherein Ip = 12(11, Icf), and Ip * Dp / Rp < Iav(M, λ) wherein Dp / Rp is the duty cycle (in [% ]).The dose D2 is then administered in a number of pulses Np, wherein Np may be approximated by Np = D2 / (Ip * Dp), neglecting relaxation and/or accustoming processes etc. The pulse duration Dp and pulse repetition rate Rp are advantageously determined such that the phototherapy dose D2 is administered in a minimum number of pulses Np and/or in a short time.

In step 25 the thus calculated phototherapy dose D2 is applied to the body portion 1 by illuminating the skin portion 3 with the optical pulses, resulting in administering the suitable dose D 1 to the body portion 1.

In calculating the pulsed irradiation to be applied, the effect of heating of the epidermis by the absorbed radiation is included, so as to determine a maximum applied irradiance in order not to overheat the skin. A skin temperature of below 42°C is considered suitable, higher temperatures, in particular during prolonged periods, are undesired and temperatures of ca 45°C and higher are painful.

Figs. 4A-4C show three different pulse shapes, having different pulse irradiances and pulse durations but having equal pulse repetition rates and providing equal doses. However, the effective deposited dose in dermal and hypodermal tissue due to the melanin absorption will generally increase from Fig. 4A to Fig. 4C and the thermal load on the epidermis will generally decrease Fig. 4A to Fig. 4C. Suitable pulse durations are between 0.02 and 100 seconds for most treatments. For a pulse duration of 0.02 seconds a pulse repetition rate of 20 pulses per second is suitable_j, assuming a dose of 20 J/cm2 and an irradiance of 20 mW/cm2. The thermal relaxation time of the epidermis is about 0.002 seconds. By varying the pulse irradiance, the pulse duration and/or the pulse repetition rate, the time-averaged irradiation, considered for a part of the treatment, may be varied as a function of time itself. This may be used to adapt a treatment to various circumstances, e.g. heating of the skin for a constant body portion absorption (energy, spectral energy distribution, characteristic time of a photochemical process) may require a decreasing repetition rate; tanning of the skin and an acceleration of a photochemical process may require an increasing pulse irradiation and decreasing pulse duration, with constant repetition rate; etc.

The method may be employed in separate stages, wherein the melanin index is determined at one moment and later on used for determining the function for operation of the light source, but since the melanin index may, and generally will, depend inter alia on the particular location of the skin portion and on its tanning, it is preferred to (re-)determine the melanin index shortly before applying a phototreatment.

As shown in Figs. 5 and 6, a phototherapy apparatus 27 for use in the above described method may comprise a light source 29 for providing light at a bio-stimulating phototherapeutic wavelength, here comprising a plurality of sub-light sources 31 mounted to a carrier 33, a sensor 35 for determining the melanin index of a subjects skin portion 3, the apparatus being arranged for illuminating the subjects skin portion 3 with light emitted by the light source 29, the apparatus further comprising a controller 37 for controlling operation of the light source 29 as a function of the determined melanin index. The apparatus 27 may be powered from any suitable power source 39, for portability, powering from a battery is preferred. The controller 37 may comprise user operable knob with selectable settings. Also or alternatively, the controller may be configured to take additional input, e.g. for determining parameters of a therapy, user settings, timing, driving schemes for different skin colors etc. Advantageously, the controller is arranged, programmable or programmed for controlling operation of the light source 29 based on the Icf function discussed above. Such program may be stored on or in a memory comprised in the apparatus.

The controller 37 may be configured for controlling operation of the light source 29 during use, possibly automated, e.g. for adaptation to skin heating, tanning, inadvertent erythema etc.

The phototherapy apparatus 27 may be a human wearable patch, such as an apparatus conforming to human physique, preferably being deformable or even pliable, indicated in Fig. 5. The patch may be maintained in position with any suitable means such as one or more adhesive portions, hook-and- loop-type fastener and/or a strap 41 closable around the body portion. Alternatively (not shown) a phototherapy apparatus may be an assembly comprising the light source, the sensor and/or the controller as separate objects, which may be interconnected for communicating with each other, e.g. with cables or via wireless communication.

A phototherapy apparatus 27 may comprise plural sensors 35 for determining the melanin index of the subject's skin portion 3 to detect local variations of the skin portion. As shown, the light source 29 may comprise plural sub-light sources 31. Advantageously, the light source 29 comprises one or more Light Emitting Diodes or LEDs, which are available for numerous suitable wavelengths, provide significant optical output power per watt input power and generate little heat. Incoherent LEDs are considered particularly advantageous, since lasers require additional control, increasing complexity and cost of the apparatus 27 and relatively narrowband radiation poses a high risk of overheating skin. Laser radiation may also present a danger to eyes of a user.

The sensor may comprise at least one light source and at least one detector for detecting light, the sensor being configured to illuminate a subject's skin portion and detect light reflected off the subject's skin portion, wherein the sensor is configured for determining a reflectivity of the subject's skin portion at a plurality of wavelengths. This allows accurate determination of the reflectance of the skin portion and thus of determining the melanin index.

Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. Features from different embodiments may be suitably combined within the scope of the appended claims, unless explicitly mentioned otherwise. "Light emitting diode" or LED includes "organic light emitting diode" or OLED. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. A single processor or other unit may fulfill the functions of several items recited in the claims. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measured cannot be used to advantage. A computer program may be stored/distributed on a suitable medium, such as an optical storage medium or a solid-state medium supplied together with or as part of other hardware, but may also be distributed in other forms, such as via the Internet or other wired or wireless telecommunication systems. Any reference signs in the claims should not be construed as limiting the scope.

Claims

CLAIMS:

1. An apparatus (27) for bio-stimulating phototherapy:

comprising a light source (29) for providing light with a phototherapeutic wavelength and a controller (37),

wherein the apparatus is configured for illuminating the skin (3) of a subject's body portion (1) with light emitted by the light source,

wherein the controller is configured to control operation of the apparatus such that the light is provided in a series of optical pulses with a controlled pulse repetition rate, with the pulses having a controlled pulse irradiance and pulse duration,

wherein the controller is further configured to control the pulse irradiance, the pulse duration and the pulse repetition rate as a function of at least one of the melanin index (M) and the lightness (L*) of the skin to provide an effective time averaged irradiance at or below a predetermined value.

2. The apparatus (27) of claim 1,

comprising an input system for determining the predetermined value of the effective time averaged irradiance.

3. The apparatus (27) of claim 1, wherein the effective time averaged irradiance value is determined as a function of the melanin index.

4. The apparatus (27) of claim 1, wherein the function comprises an irradiance correction factor Icf = exp(Cm μ(λ) d), with:

Cm = (M-20)/150, or Cm = 1.925 - 0.44 ln(L*), μ(λ) = μ₀ λ^{"3 3} = 6.6 x 10¹¹ λ^{"3 3} cm^"1, and d is selected from a range of 0.004-0.024 cm,

wherein Cm is a measure of the concentration of melanonosomes in the epidermis of the skin portion (3), M is the melanin index, and L* is the lightness of the skin portion (3), respectively, μ(λ) is the wavelength dependent absorption coefficient of the melanin (in units of cm^"1 with λ in units of nm), and d accounts for the optical path in the epidermis (in units of cm).

5. The apparatus (27) of claim 1, wherein the light source (29) comprises one or more light emitting diodes (31).

6. The apparatus (27) of claim 1, wherein

at least a portion of the apparatus is formed to conform to at least part of the subject's body portion (3).

7. The apparatus (27) of claim 1, comprising at least one sensor for non- invasively determining at least one of the melanin index (M) and the lightness (L*) of the subjects skin portion (3).

8. The apparatus (27) of claim 7, comprising at least one further sensor for determining at least one further skin parameter.

9. The apparatus (27) of claim 1, wherein the controller (37) is at least one of configured or configurable to control at least one of the pulse irradiance, the pulse duration and the pulse repetition rate as a function of time during operation of the light source.

10. The apparatus (27) of claim 1 wherein the controller is programmable.

11. A method of bio-stimulating phototherapy of a subject's body portion comprising the steps of

determining a bio-stimulating wavelength range to be administered;

determining a first irradiance to be applied;

determining at least one of the melanin index (M) and the lightness (L*) of the skin (3) of the body portion (1),

determining a second irradiance as a function of the first irradiance, the wavelength range and the melanin index or the lightness, respectively;

providing a number of optical pulses of the determined wavelength range to the body portion, each pulse having a pulse irradiance, a pulse duration and a pulse repetition rate;

wherein the pulse irradiance, the pulse duration and the pulse repetition rate are controlled as a function of the melanin index of the skin and an effective time averaged irradiance at or below a predetermined value is provided.

12. The method of claim 11, wherein the predetermined value of the effective time averaged irradiance is determined as a function of at least one of the melanin index (M) and the lightness (L*).

13. Method of claim 11, wherein the function comprises an irradiance correction factor Icf = exp(Cm μ(λ) d), with: